1. Field of the Invention
The invention relates to a data compression apparatus for data compressing an audio signal, a data compression method, a transmitter comprising the data compression apparatus, a recording apparatus comprising the data compression apparatus, a record carrier having the data compressed audio signal recorded in a track of said record carrier, a data expansion apparatus for data expanding a data compressed audio signal, a data expansion method, a receiver comprising the data expansion apparatus and a reproducing apparatus comprising the data expansion apparatus.
2. Description of the Related Art
Data compression on an audio signal is well known in the art. Reference is made in this respect to European Patent Application No. EP-A 402,973, corresponding to U.S. Pat. Nos. 5,323,396; 5,530,655; 5,539,829; 5,606,618; 5,777,992; and 6,691,086. This patent describes a subband coder, in which an audio signal is A/D converted with a specific sampling frequency, such as 44.1 kHz, and the resulting samples, in the form of, e.g., 24-bit words of the audio signal, are supplied to a subband splitter filter. The subband splitter filter splits the wideband digital audio signal into a plurality of relatively narrow band subband signals. Using a psycho-acoustic model, a masked threshold is derived and blocks of samples of the subband signals are subsequently quantized with a specific number of bits per sample for each block of the subband signals in response to said masked threshold, resulting in a significant data compression of the audio signal to be transmitted. The data compression carried out is based on ‘throwing away’ those components in the audio signal that are inaudible and is thus a lossy compression method. The data compression described in the above patent is a rather intelligent data compression method and requires a substantial number of gates or instructions when realized in hard or software, respectively, so that it is expensive. Moreover, the subsequent expansion apparatus also requires a substantial number of gates or instructions, when realized in hardware or software, respectively.